Implantable sensor enclosure with thin sidewalls

ABSTRACT

A wireless circuit includes a housing, such as a hermetic housing, and at least one antenna coil wound about a coil axis within the housing. The coil axis may be substantially parallel to at least one wall of the housing, wherein the wall parallel to the coil axis is substantially thinner than other walls of the housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application PCT/US2012/044998entitled “IMPLANTABLE SENSOR ENCLOSURE WITH THIN SIDEWALLS” filed onJun. 29, 2012 which claims benefit of Provisional Patent Application No.61/502,982 entitled “IMPLANTABLE SENSOR ENCLOSURE WITH THIN SIDEWALLS,”filed on Jun. 30, 2011, which are hereby incorporated by reference inits entirety

FIELD OF INVENTION

This application relates to implant packages and more particularly to animplantable sensor enclosure with thin sidewalls.

BACKGROUND

Implantable wireless sensors are useful in assisting diagnosis andtreatment of many diseases. Examples of wireless sensor readers aredisclosed in U.S. patent application Ser. No. 12/737,306 entitledWireless Sensor Reader, which is incorporated by reference herein.Delivery systems for wireless sensors are disclosed in PCT PatentApplication No. PCT/US2011/45583 entitled Pressure Sensor, CenteringAnchor, Delivery System and Method, which is also incorporated herein byreference. In particular, there are many applications where measuringpressure from within a blood vessel deep in a patient's body isclinically important. For example, measuring the pressure in the heart'spulmonary artery is helpful in optimizing treatment of congestive heartfailure. In this type of application, a sensor may need to be implanted10 to 20 cm beneath the surface of the skin.

Wireless sensors that use radiofrequency (R1) energy for communicationand/or power have been found to be particularly useful in medicalapplications. However, a key challenge in successful commercializationof these implantable wireless sensors is the design tradeoff betweenimplant size and the “link distance”, which is the physical distancebetween the implant and the external device communicating with theimplant. From a medical standpoint, it is desirable for an implant to beas small as possible to allow catheter based delivery from a smallincision, implantation at a desired location, and a low risk ofthrombosis following implant. However, from a wireless communicationstandpoint, the smaller the implant, the shorter the link distance. Thisdistance limitation is driven primarily by the size of the antenna thatcan be realized for a given overall implant size. A larger antenna isbetter able to absorb RF energy and transmit RF energy than a smallerantenna. For example, in the case of wireless communication viainductive coupling, a typical implant antenna has the form of a coil ofwire. The coil's “axis” is the line that extends normal to the plane ofthe windings, i.e. the axis is perpendicular to the wire's length. Asthe area encircled by the coil increases, the amount of magnetic fluxthat passes through it generally increases and more RF energy isdelivered to/received from the implant. This increase in flux throughthe implant antenna can result in an increase in link distance. Thus toachieve maximum link distance for a given implant size, the implantantenna should be of maximal size.

While antenna size is important, other implant architectures may benefitfrom maximizing the size of other internal components. An implantcontaining an energy storage device such as a battery, for example,would enjoy longer battery lifetime with a larger battery. In anotherexample, a drug-eluting implant could hold a larger quantity of thedrug. Other examples will be apparent to those skilled in the art.

Another challenge in commercialization of implantable wireless sensorsis the need to protect the sensitive sensor electronics from potentiallycorrosive or damaging fluids of the body. For many implant applications,the sensor may need to record accurate measurements for a period of timeexceeding 7 to 10 years. Small changes in electrical, chemical, ormechanical properties of the implant over this time period can result ininaccurate measurements. To prevent inaccurate measurements, a hermeticenclosure may be required to protect the sensitive electronics of thesensor from the transfer of liquids and gases from the bodilyenvironment.

Hermetic enclosures for implants are typically constructed of metals,glasses, or other ceramics. Metals are malleable and machineable,capable of being constructed into thin walled hermetic enclosures suchas the titanium enclosures of pacemakers. Unfortunately, the use ofmetals in hermetic enclosures may negatively impact the ability of thesensor to communicate wirelessly with an external device, especiallywhen communication at low radiofrequencies is desired. While ceramicsand glasses are compatible with wireless RF communication, it isdifficult to machine ceramics to a thin walled hermetic enclosure. Thebrittleness of ceramics prevents the construction of thin wall hermeticenclosures from ceramic materials.

State of the art ceramic machining can produce walls of approximately0.5-0.7 mm thickness. For implants whose length, width, and heightdimensions are typically ones of millimeters, this can represent asignificant reduction in available internal volume for components suchas antennas.

Hermetic enclosures known in the art, particularly those made of ceramicand/or glass materials, do not lend themselves to efficient use oflimited space. Non-metal hermetic enclosures known in the art aretypically manufactured via planar processing technology, such as lowtemperature cofired ceramic processes, laser machining, ultrasonicmachining, Electronic Discharge Machining (EDM), or Micro ElectroMechanical Systems (MEMS) fabrication techniques. These techniques arecapable of processing ceramics and glasses with tight control of featureresolution. However, sidewalls of an implant package made with thesetechniques often require use of a dicing saw or laser to separate theimplant package from the remaining substrate. Due to manufacturingconstraints and the need for mechanical strength, implant packagesidewalls made by these methods are typically 0.3 mm-0.5 mm thick.Alternative manufacturing approaches, such as the molding or machiningof ceramic, are typically limited to minimum sidewalls of 0.5-0.7 mmthick.

An example of a prior art hermetic implant package 10 is shown inFIG. 1. The implant package 10 includes thick sidewalls 12 that limitthe space available for the internal components, in this case implantantenna 14. For example, an implant package of width 4 mm that hassidewalls 0.5 mm thick only has a maximum of 3 mm of width available foran implant antenna. FIG. 1 shows an antenna 14 that is placed into theimplant package from an opening at the top of the package. To completethe implant package, a top layer 16 is connected or bonded to theimplant package and sealed as shown in FIG. 2A. For pressure-sensingimplant packages known in the art, the top layer is typically either acapacitive pressure sensor itself, a thin membrane that is directly partof a sensing electronic circuit, or a thin membrane that communicatespressure from the environment to the inside of the implant package viaan incompressible liquid or gel. Manufacturing techniques known in theart are capable of routinely processing membranes to thicknesses of0.025-0.1 mm. Many variations of the FIG. 1-2 architecture exist in theprior art, including the method of etching a cavity in half of a housingto create the thin wall on top of the coil, and then bonding the twohousing halves vertically. This is depicted in the sketch of FIG. 2B,where the upper housing half 999 has a cavity etched into it to createthe thin membrane.

Other prior art exemplifies wireless implant architectures of the typeshown in FIG. 1 and FIG. 2, where the thin pressure sensitive membraneis in a plane that is perpendicular to the coil's axis. U.S. Pat. No.7,574,792 (O'Brien), U.S. Pat. No. 6,939,299 (Petersen), and U.S. Pat.No. 4,026,276 (Chubbuck) all teach implantable pressure sensors withcoil antennas, and hermetic housings with at least one deformablepressure-sensitive wall. In all these cases, the pressure-sensitivewalls of the housings are perpendicular to the coil axis, and the wallslocated outside the coil perimeter are rigid, structural, and relativelythick. In these architectures, total coil area is limited by the needfor a relatively thick structural wall outside the coil perimeter.

To improve implantable wireless sensors, it is desirable to have ahermetic enclosure with thin walls outside the coil antenna perimeter,thus maximizing the internal dimension that most constrains antennasize.

SUMMARY OF THE INVENTION

This application relates to hermetically packaged wireless electronicsand more particularly to implantable electronics enclosures with thinsidewalls to maximize an internal dimension.

In an embodiment, a wireless circuit includes a housing and at least oneantenna coil wound about a coil axis within the housing. The coil axismay be substantially parallel to at least one wall of the housing,wherein the wall parallel to the coil axis is substantially thinner thanother walls of the housing. The housing may be a hermetically sealedhousing.

In an embodiment, the wireless circuit may be manufactured by forming ahousing of a material with at least one open side. Electronics,including an antenna coil, may then be placed into the housing such thatsaid antenna coil's axis is substantially parallel to the plane of atleast one open side. A wall that is substantially thinner than the wallsof the housing may then be bonded to the open side. The wall may behermetically bonded or otherwise bonded as known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 illustrates a prior art implant package, not including the finalsealing layer;

FIG. 2A illustrates a typical prior art implant package, including athin sealing layer;

FIG. 2B illustrates a typical prior art implant package, with a cavityetched into part of the housing;

FIG. 3A illustrates the housing portion of a hermetic wireless packageof the present invention;

FIG. 3B illustrates the complete hermetic wireless implant of thepresent invention;

FIG. 4A illustrates the housing portion of an alternative embodiment ofthe present invention, with etched cavities and a split housing;

FIG. 4B illustrates the assembly of an alternative embodiment of thepresent invention, with etched cavities and a split housing;

FIG. 4C illustrates the completed implant, for an alternative embodimentof the present invention, with etched cavities and a split housing;

FIG. 5A is an exploded sketch of another alternative embodiment of thepresent invention, with electronics bonded to the top of the housing;

FIG. 5B illustrates the completed alternative embodiment of the presentinvention, with electronics bonded to the top of the housing;

FIG. 6 illustrates another alternative embodiment of the presentinvention, with electronics bonded to the side of the housing;

FIG. 7 illustrates another alternative embodiment of the presentinvention, with electronics contained in a separate housing chamber

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. It is tobe understood that other embodiments may be utilized and structural andfunctional changes may be made without departing from the respectivescope of the invention.

This application relates to implant packages and more particularly to animplantable sensor enclosure with thin sidewalls. To facilitate maximumlink distance for a given implant size, the enclosure should beconstructed to maximize antenna coil area, while still providing ampleprotection.

The implant package may utilize thin membrane materials such as glass,quartz, sapphire, fused silica, alumina, titanium, diamond, or othermaterials known in the art, to increase the space available inside animplant package of a fixed outer size. Whereas in prior art implantpackages the thin membrane is bonded to the top of the implant package,as in FIGS. 1 and 2, the thin membrane or membranes may be bonded to theside of the implant package, such that they are in a plane substantiallyparallel with the axis of the coil, as in FIG. 3.

FIGS. 3A-3C show basic assembly steps for a wireless implant package 20that maximizes coil area by its wall arrangement. The implant in theFigure has the long, narrow, rectangular shape of a typicalcardiovascular implant, although the principle applies to any geometry.FIG. 3A illustrates the basic housing 300 in side view (long dimension)and front view (short dimension) cutaway. In an embodiment, thedimension of housing 300 may be generally cuboid and defining a volumetherein. The housing side walls may be of specific dimensions andproportions to each other. For example, the housing may have four walls(‘top’, ‘bottom’, ‘front’, and ‘back’), but two of the long sides may beopen, so that one can look through the housing into the page in the FIG.3A side view. As described herein, the length of the housing side wallsrefers to the longer dimension of the open walls (also corresponding tothe longer dimension of the top and bottom walls of the housing asillustrated in the Side View of FIG. 3A.) The height and width of thehousing refers to the dimensions of the remaining sidewalls or the topand bottom walls as illustrated in the Front view of FIG. 3A. Dimensionsprovided below list the dimensions of the housing in the order of(length×width×height). The length of the housing may be at leasttwo-times greater than the width and height dimensions. By way of anon-limiting example, the dimensions of the housing may be approximately25×3.75×2.25 mm, with walls 0.5 mm thick. Housing 300 may be made of ahermetic, strong, and biocompatible material, such as ceramic. Suchhousings are fabricated with processes well known in the art, includingmicromachining, ultrasonic machining, wet etching, plasma etching, orlaser machining. While examples are made to a cuboid housing, it will beappreciated that other shapes and configurations may be used, such ascylindrical housings, prism-shaped housings, octagonally or hexagonallycross-sectioned housings, or the like.

In other embodiments the length of the implant housing may have valuesof 5, 10, 15, 20, 25, or 30 mm long. The cross sections may havewidth×height values of 5×3 mm, 4.5×2.25 mm, 3.25×2.25 mm, 2.5×1.75 mm,or 2×1 mm.

In FIG. 3B, an antenna coil 14, also shown in cutaway, is placed intothe housing 300 via the open walls on the long side. Microelectronics301, which may include one or more pressure sensors, may also be placedinside housing 300, inside the region encircled by coil 14, or outsideof this region.

FIG. 3C depicts the final step, in which thin walls 302 are bonded tohousing 300, such as hermetically bonded. It will be appreciated thatthe thin walls 302 may be sealed or bonded in any appropriate manner. Itwill also be appreciated that the concepts herein may apply tonon-hermetic housing applications, such as acute implants. In thesecases, non-hermetic materials and bonding methods known in the art maybe used. As illustrated and described in the examples herein, the thinwalls 302 may be substantially thinner, or include a portion that issubstantially thinner, than the remaining walls of the housing.Non-limiting examples of wall thicknesses of the housing walls and thinwalls 302 are provided below. By orienting the thin walls 302 such thatthey are parallel to the axis 303 of coil 14, the width of coil 14 inthe short dimension (left to right in the front view) is maximized. Inthis way, the implant package can achieve the maximum possible coil looparea within the width constraint imposed on the short dimension. It willbe appreciated that the coil axis 303 refers to the central axis of agenerally spirally wound coil 14, as shown in FIG. 3. The spirally woundcoil 14 may be any appropriate shape, such as circular, rectangular, orany other shape.

The final implant produced by the process of FIG. 3 meets the complexrequirements of medical implants: (i) small cross-sectional area, (ii)non-metal housing, (iii) hermetic sealing, (iv) biocompatibility, and(v) maximum internal volume for a given external volume.

In the case where wireless implant 20 contains a pressure sensor,internal electronics 301 may include one or more pressure sensors knownin the art, and thin walls 302 may be flexible membranes whichcommunicate pressure to internal electronics 301 by means of anincompressible fluid or gel that fills the cavity formed by housing 300and thin walls 302. In another embodiment, the thin walls 302 may beflexible membranes which are part of a sensing electronic circuit, thustransducing pressure directly into an electronic signal of a sensingcircuit.

The walls of the housing other than the thin walls 302 may be greaterthan 0.3 mm. By comparison, in an embodiment, by using membranes as thethin sidewalls 302 of the implant package 20 each sidewall may have athickness of less than 0.15 mm. In another embodiment, by usingmembranes as the thin sidewalls 302 of the implant package 20 eachsidewall may have a thickness less than about 0.050 mm. In anotherembodiment, by using membranes as the thin sidewalls 302 of the implantpackage 20 each sidewall may have a thickness of about 0.025 mm. Inanother embodiment, by using membranes as the sidewalls of the implantpackage 302 each sidewall may have a thickness less than about 0.025 mm,such as about 0.020 mm, about 0.015 mm, about 0.010 mm, about 0.005 mm,about 0.001 mm and any sized thickness in between. Thus, the thin walls302 may have one half or less of the thickness of the non-thin walls ofthe housing 20.

In a typical embodiment, thin walls 302 may be made of one or more thinfilm materials such as glass, quartz, fused silica, titanium, silicon,sapphire, diamond, or others. It may be thinned by polishing, etching,or other methods well known in the art. Thin walls 302 may be bonded tohousing 300 by several means known in the art, including laser welding,glass frit bonding, or compression bonding by brazing, soldering, oreutectic bonding, following deposition of a metal braze ring on the twosurfaces.

For bonding technologies that require a metal ring to be depositedaround the perimeter of each diaphragm, on both the diaphragm and matingsurfaces on the housing, the architecture of FIG. 3C provides a furtheradvantage over the prior art. When the metal ring is parallel to theantenna windings, as in prior art FIG. 1, it may absorb and dissipatesignificant amounts of energy going to and coming from the antenna 14,due to shielding and eddy current formation. However, when the diaphragmbonding rings are arranged perpendicular to the antenna windings as inFIG. 3C, the shielding and eddy current effects are practicallyeliminated.

The thin-walled housing or implant package 20 provides a significantimprovement in the efficient use of space inside an implant package overprior art. By way of a non-limiting example, for a prior art implantpackage having an outer width of about 4 mm, the maximum available widthfor the antenna was approximately 3 mm. By contrast, in a thin-walledimplant package 20 with an outer width of about 4 mm, the availablewidth for the antenna is approximately 3.95 mm. Such an increase inantenna width for a given implant outer size may dramatically increasethe wireless link distance of an implantable wireless sensor. Thisdifference in antenna width of the thin-walled implant package 20 cantranslate into a catheter delivery system that is about 3 Fr sizessmaller for the present invention than for prior art systems.

The invention is thus particularly useful in wireless implants that haveone axis longer than the others, which is generally the case forimplants that are intended for placement in blood vessels, or intendedfor delivery through a catheter device. If the ratio of length to widthof such an implant is x, then increasing the coil's width dimension by nmicrons creates more coil area than the same increase in the lengthdimension, by a factor of x. In such wireless implants, one cangenerally maximize coil area by placing the thinnest sidewalls parallelto the coil axis, and perpendicular to the shorter dimension, as in FIG.3C.

It will be further appreciated that the implant architecture can be usedto maximize the size of any internal component, substance, orcombination thereof. These may include, but are not limited to, drugs,steroids, batteries, stimulus electrodes, pacing circuitry, flowsensors, chemical sensors, or other electronics.

It will be further appreciated that although the exemplary embodimentsdepict a rectangular coil, the coil 14 can be generally circular,ovular, rectangular, or can take the form of any polygon that enclosesan area. Additionally, although a rectangular housing is shown in theexemplary embodiment figures, the concept of disposing the thin walls onthe outer periphery of coil 14, parallel to coil axis 303, can begeneralized to any polygonal shape.

The disclosed invention depicted in FIG. 3 may have a further benefitfor pressure sensing implants. Many commonly available chip-scalepressure sensors are well suited for use in wireless implants. However,such pressure sensors generally have small, thin, pressure sensingdiaphragms, on the order of 2 mm diameter or less and thickness of 500nm or less. If such a diaphragm is exposed to living tissue or blood,one or more layers of cells will usually grow on it after a period ofseveral days or weeks. Cell layers such as this are known to stiffen thesensor's diaphragm, decreasing the device's sensitivity. In theembodiment shown in FIG. 3C, the thin sidewalls 302 may serve asflexible pressure diaphragms, which communicate pressure to chip-scalepressure sensors on internal electronics 301 through apressure-communicating medium. Because they are larger in area andgenerally stiffer than the diaphragms of chip scale sensors, the thinsidewalls 302 will not be stiffened significantly by several layers ofcell growth, compared to the smaller diaphragms of the chip-scalesensors. Thus the present invention allows pressure sensor implantdesigners to select from a number of available off-the-shelf or customchip-scale pressure sensors, without having to worry about diaphragmstiffening due to cell growth.

While the thin-walled implant package 20 may be used with R1 medicalimplants, the designs set forth herein are useful for any micro deviceor component where a non-metal hermetic enclosure is required and whereit is desirable to minimize sidewall thickness. Examples include, butare not limited to, sensors, actuators, or transponders located in harshchemical environments, in liquid immersion, in high temperature zones(such as engines), or in environments where sterility is critical. Otherexamples include applications where the internal electronics must behermetically housed, but cannot tolerate shielding or eddy currentlosses imposed by metal housings or braze rings. The designs and methodsdescribed herein overcome the many challenges associated with wirelesssensors that use radiofrequency.

There are also numerous variations of the embodiment shown in FIG. 3.For example, as shown in FIG. 4A, the housing is formed in two pieces401 and 402, each with a cavity formed by one of the micromachiningprocesses known in the art. The location of the cavity is shown as adotted line in the side view, and can be seen in the cutaway. As shownin FIG. 4B, the coil 14, electronics 301, and other internals areinserted into one of the housing pieces 401. As shown in FIG. 4C,housing pieces 401 and 402 are bonded together hermetically by one ofthe methods previously disclosed. Note that in FIGS. 4A-4C, housingpieces 401 and 402 are shown as symmetrical, but asymmetrical pieces mayalso be employed.

FIGS. 5A and 5B depict an embodiment in which the electronics 501 arefabricated as a thin film device by one of the processes known in theart, with FIG. 5A being an exploded view and FIG. 5B showing all partsassembled. In FIGS. 5A and 5B, housing 500 has its long sides open asbefore, but this time its top side is open. Coil 14 is then insertedinto housing 500. The thin film electronics device 501 is connected tocoil 14 by wirebonding, conductive adhesive, or other means known in theart, and electronics 501 are then hermetically bonded to housing 500using one of the aforementioned processes. Electronics 501 now forms thetop surface of the housing. Thin sidewalls 502 are hermetically attachedto housing 500 as before. If the thin electronics 501 contain a pressuresensor, the internal volume of the housing may not need to be filledwith an incompressible fluid, as thin sidewalls 502 do not need tocommunicate pressure. Additionally, it will be appreciated that thesteps of bonding electronics 501, bonding each of thin sidewalls 502, orinserting coil 14, may be done in a different order. The electronics 501may be a single, solid state device, such as a capacitive sensor, or itmay be multiple devices attached to a hermetic substrate such as LTCC.

FIG. 6 illustrates an embodiment similar to that of FIG. 5. Theelectronics 601 are placed on the exterior of housing 600, but this timeon one of the short ends. FIG. 6 depicts hermetic electricalfeedthroughs connecting electronics 601 to coil 14, but a ‘free wire’connection method such as the one depicted in FIGS. 5A and 5B may alsobe employed. As in FIGS. 5A and 5B, the thin sidewalls 302 are notcommunicating pressure and so incompressible liquid fill may not berequired.

FIG. 7 illustrates an embodiment similar to that of FIG. 6. Here thehousing has two chambers, one for the coil and another for theelectronics (shown here as “Sensor” and “Substrate”). The coil andelectronics connect via a feedthrough that may or may not be hermetic.Thin sidewalls are placed in the usual place on the sides of the coil,and again over the chamber that contains the electronics. If theelectronics does not contain a pressure sensor, the sidewall over theelectronics chamber may be a thicker wall or a thin wall of a stiffermaterial. If the electronics contains a pressure sensor, and if theelectrical feedthrough is sufficiently leak tight, then only the chambercontaining the sensor needs to be filled with incompressible fluid.

The invention disclosed herein is particularly advantageous when thewireless implant is required to be long and narrow, as is typically thecase with cardiovascular implants. With such geometries, any coil widthgained in the short dimension has a dramatic impact on coil area andhence link distance.

Many of the embodiments disclosed herein may benefit from having thefinal sidewalls attached in a vacuum environment, to prevent internalpressures inside the housing from varying with temperature.Alternatively, the internal volume may be filled with an inert gas tolimit corrosion of the internals.

It will also be appreciated that the implant housing embodimentsdisclosed herein can be made using all thick walls, and thenpost-processing the housing to thin portions of the walls that areparallel to the coil's axis. State of the art post-processingtechnologies such as grinding, polishing, etching, or laser ablation aresome possible means for accomplishing this.

In all embodiments, the external housing may be surface treated with abiocompatible material to limit clot formation, control cell growth, orimprove lubricity. Such materials may include heparin, silicone,parylene, cell tissue monolayers, or other coatings well known to thoseof ordinary skill in the art.

While the apparatus and method of subject invention have been shown anddescribed with reference to preferred embodiments, those skilled in theart will readily appreciate that changes and/or modifications may bemade thereto without departing from the spirit and scope of the subjectinvention.

Having thus described the invention, we claim:
 1. A wireless circuitcomprising: a housing; at least one antenna having an axis andpositioned within said housing; wherein said axis is substantiallyparallel to at least one wall of said housing; and wherein said at leastone wall is thinner than at least one wall of said housing that is notsubstantially parallel to said coil axis.
 2. The wireless circuit ofclaim 1, wherein said housing has length, width and height dimensions,and wherein the length is greater than the housing's width and heightdimensions.
 3. (canceled)
 4. The wireless circuit of claim 1, whereinsaid wireless circuit is configured to measure pressure.
 5. The wirelesscircuit of claim 4, wherein said substantially thinner wall isconfigured to deform in proportion to pressure exerted on it.
 6. Thewireless circuit of claim 1, wherein said wireless circuit contains abattery.
 7. The wireless circuit of claim 1, wherein said at least onewall which is substantially parallel to said coil axis comprises amaterial selected from a group including: sapphire, fused silica,quartz, glass, ceramic, titanium, alumina, silicon, diamond, andpolymer.
 8. The wireless circuit of claim 1, wherein said at least onewall which is substantially parallel to said coil axis is created byforming a cavity in at least one part of said housing prior to bondingsaid at least one part to other parts of said housing.
 9. The wirelesscircuit of claim 1, wherein said at least one wall which issubstantially parallel to said coil axis is created by bonding amaterial to said housing.
 10. The wireless circuit of claim 1, whereinsaid at least one wall which is substantially parallel to said coil axisis created by thinning at least a portion of said wall after parts ofsaid housing have been bonded together.
 11. The wireless circuit ofclaim 1, wherein portions of said housing are bonded together by aprocess selected from a group including: laser welding, glass fritbonding, laser frit welding, compression bonding, anodic bonding,eutectic bonding, brazing, or soldering.
 12. (canceled)
 13. The wirelesscircuit of claim 1, wherein a portion of said wireless circuit serves asone of the walls of said housing that is not substantially parallel tosaid coil axis.
 14. The wireless circuit of claim 1, wherein a portionof said wireless circuit is disposed on one of the walls of said housingthat is not substantially parallel to said coil axis.
 15. The wirelesscircuit of claim 1, wherein a portion of said wireless circuit isdisposed in a portion of said housing separate from the portion thatcontains said antenna coil.
 16. The wireless circuit of claim 1, whereinsaid housing is filled with a substance selected from a group including:liquid, gel, vacuum, inert gas, or air. 17-21. (canceled)
 22. Thewireless circuit of claim 1, wherein said antenna having an axisincludes a coil.